Battery pack

ABSTRACT

A battery pack ( 10 ) includes: a battery ( 1 ); a circuit substrate ( 5 ) having a charge/discharge safety circuit and arranged on one end face ( 3 ) of the battery; and an end case ( 6 ) in which an external connection terminal ( 7 ) is set. In this battery pack, the circuit substrate ( 5 ) is arranged inside the end case ( 6 ), and the end case ( 6 ) is secured to the battery by screws ( 12 ) with a screw head ( 12   a ) extending through and engaging with the end case ( 6 ) at both ends and tips of the screw ( 12 ) being engaged into the end face ( 3 ) at both ends of the battery ( 1 ). This achieves a compact battery pack with a reduced connection resistance, while achieving both high reliability and productivity.

TECHNICAL FIELD

The present invention relates to a battery pack made by coupling abattery and an end case into one piece, the end case accommodating acircuit substrate that includes a charge/discharge protection circuitand is arranged at one end of the battery.

BACKGROUND ART

A battery pack which is formed by uniting a circuit substrate having acharge/discharge protection circuit with a battery is required to have acompact structure, low connection resistance, high reliability ofconnected parts, and high production efficiency.

Conventional battery packs are structured such that the battery isaccommodated inside a case with a protection element and a circuitsubstrate. To give an example, there is known a battery pack wherein abattery is accommodated in a case having a terminal window, and aprotection element and a circuit substrate are arranged in a spaceprovided between the battery and the case. A lead plate that connectsthe battery with the circuit substrate is arranged opposite the terminalwindow to serve as an external terminal (see, for example, Prior ArtDocument 1).

Another known battery pack uses a terminal holder having a fittingprotrusion at the bottom that fits into a recess on a battery that isformed by the protruding periphery of one end face of the battery. Aprotection element is set inside the terminal holder, and a terminalplate is secured to the top face of the holder. After the terminalholder is coupled to the battery with an adhesive tape or heat shrinkfilm, a lead plate that will extend to the outside is welded to theterminal plate and the battery case, and the holder and the battery areeither accommodated in a case or covered by a heat shrink tube or thelike to constitute a battery pack (see, for example, Prior Art Document2).

In yet another known battery pack, the sealing plate of the batteryincludes a connection boss that is coupled to the circuit substrate soas to connect the battery and the circuit substrate both mechanicallyand electrically (see, for example, Prior Art Document 3), which iscontrary to the conventional practice of connecting the battery and thecircuit substrate mechanically and electrically with a lead plate, withthe circuit substrate being temporarily held on the battery using aholder.

In another known battery pack, the battery is partly or entirelyinsertion molded such that an external connection terminal is exposed tothe outside, and a resin mold in which a protection element is fixedlyset is formed in one piece with the battery at its one end (see, forexample, Prior Art Document 4).

Prior Art Document 1: Japanese Patent No. 3244400

Prior Art Document 2: Japanese Patent Publication No. 2000-243362

Prior Art Document 3: Japanese Patent Publication No. 2002-298809

Prior Art Document 4: Japanese Patent Publication No. 2004-95329

In the structure shown in Prior Art Document 1, however, because thereis provided a space between the case and the battery for placing theprotection element and the circuit substrate, the case is large. Whilethere is the risk that the circuit substrate or protection element maybe damaged by vibration, it is hard to retain them in position to thebattery or case, and high reliability is hard to achieve. Further, theconnection resistance is high because of the use of a lead plate.

In the structure shown in Prior Art Document 2, a protection element issecurely attached to the battery through the terminal holder. A leadplate is welded to the assembly of this battery and holder, which isthen accommodated in a case to form the battery pack. Therefore thebattery pack is large in size and has high connection resistance. Also,it requires a large number of assembling process steps, because of whichhigh productivity is hard to achieve.

In the structure shown in Prior Art Document 3, the circuit substrate issecured to the battery using a special sealing plate that has aconnection boss so that connection is established without using a leadplate to reduce the connection resistance and the number of assemblingprocess steps. However, these circuit substrate and battery are thenaccommodated in a case to form the battery pack and therefore it islarge in size.

In the structure shown in Prior Art Document 4, the battery, theprotection element, and the output terminal are insertion molded so thatthe protection element and the output terminal are secured in the resinmold. With this structure, the number of components is fewer and thebattery pack is compact, but insertion molding presents other problemssuch as high equipment cost and difficulties in achieving highdimensional precision and high productivity.

Accordingly, in view of the above-described problems in conventionaltechniques, it is an object of the present invention to provide acompact battery pack having low connection resistance, high reliability,and high productivity.

DISCLOSURE OF THE INVENTION

To achieve the above object, the present invention provides a batterypack including a battery, a circuit substrate having a charge/dischargesafety circuit and arranged on one end face of the battery, and an endcase in which an external connection terminal is set, wherein thecircuit substrate is arranged inside the end case, and the end case issecured to the battery by screws with a screw head, the screw headextending through and engaging with the end case at both ends and tipsof the screw being engaged into the end face at both ends of thebattery.

With this structure, the battery pack is made compact since it onlyrequires the end case secured to one end of the battery, and also theconnection resistance is reduced because the connection path between thebattery and the circuit substrate and the external connection terminalinside the end case is made shorter. Further, the battery and the endcase are securely coupled together by a simple process step of engagingthe tip of the screw into the end face of the battery, and therefore thebattery pack achieves both high reliability and productivity. Since theend case is secured to the battery with screws, the battery pack resistsa large force applied in a direction parallel to the end face of thebattery (shear direction to the screw), as well as a large force thatacts to separate the end case from the battery (screw pullingdirection), and therefore the battery pack exhibits high attachmentstrength to external forces from all directions.

The present invention also provides a battery pack including a battery,a circuit substrate having a charge/discharge safety circuit andarranged on one end face of the battery, and an end case in which anexternal connection terminal is set, wherein the circuit substrate isarranged inside the end case, and the end case is secured to the batteryby coupling pins with heads, the heads of the coupling pins extendingthrough and engaging with the end case at both ends and the tips of thecoupling pins being secured to the end face at both ends of the battery.

With this structure, the battery pack is made compact since it onlyrequires the end case secured to one end of the battery, and also theconnection resistance is reduced because the connection path between thebattery and the circuit substrate and the external connection terminalinside the end case is made shorter. Further, the battery and the endcase are securely coupled together by a simple process step of securingthe tip of the coupling pin to the battery, and therefore the batterypack achieves both high reliability and productivity.

The end face of the battery at least in a portion thereof to which thetip of the coupling pin is attached may be provided with the same typeof material as the coupling pin, so that the joint has sufficientstrength and high reliability because the materials joined together areof the same type. For example, when the end face of the battery is madeof aluminum or an aluminum alloy as with the battery case while thecoupling pin is made of an iron material so as to secure sufficientstrength despite its small size, there may be cases where, by aresistance welding method, it is hard to achieve necessary attachmentstrength with high reliability. If the end face of the battery in aportion where the tip of the coupling pin will be attached is made ofthe same material as the coupling pin, then a highly reliable joint isreadily achieved.

The method of providing the portion in one end face of the batteryopposite the tip of the coupling pin with the same material as thecoupling pin includes forming the end face of the battery using acompound material such as a clad plate of aluminum or an aluminum alloyand steel plate bonded together, and securely attaching the samematerial as the coupling pin to the material forming the end face of thebattery by laser welding or electronic beam welding. Preferably, andmore easily, a screw that is made of the same material as the couplingpin may be tightened to the battery.

The present invention also provides a battery pack including a battery,a circuit substrate having a charge/discharge safety circuit andarranged on one end face of the battery, and an end case in which anexternal connection terminal is set, wherein the circuit substrate isarranged inside the end case, and the end case is secured to the batteryby a coupling pin with head, the head extending through and engagingwith the end case, such that the material forming the end face of thebattery bites into a recess formed in an outer periphery at the tip ofthe coupling pin to secure the tip of the coupling pin to the end faceof the battery.

With this structure, the battery pack is made compact since it onlyrequires the end case secured to one end of the battery, and also theconnection resistance is reduced because the connection path between thebattery and the circuit substrate and the external connection terminalinside the end case is made shorter. Further, the coupling pin issecurely engaged with the end face of the battery such that the materialforming the end face of the battery bites into a recess formed in theouter periphery at the tip of the coupling pin. Therefore, as comparedto the case where the coupling pin is merely secured to the end face ofthe battery at the tip, the battery pack resists a large force appliedin a direction parallel to the end face of the battery (shear directionto the pin) and a large force that acts to separate the end case fromthe battery (pin pulling direction). The battery pack thus has highattachment strength to external forces from all directions and has highreliability.

Preferably, the coupling pin should include a protrusion at the tip thathas the recess in its peripheral surface, and the end face of thebattery should include a hole to which the protrusion at the tip of thecoupling pin fits, and with the protrusion being fitted in the hole, thetip of the coupling pin and the end face of the battery are joinedtogether by resistance welding, so that the material forming the endface of the battery melts by the resistance welding operation and bitesinto the recess and the battery and the end case are firmly unitedtogether as described above. Thus highly reliable battery pack is formedwith a simple process using resistance welding, and productivity andhigh reliability are both achieved.

Preferably, the battery case serves as an electrode terminal of onepolarity and an electrode terminal of the other polarity is provided onthe end face in the battery. A first connection bracket having anupright portion is secured to the end face of the battery case, aconnection plate that makes surface contact with the upright portion ofthe first connection bracket and that is partly connected to the circuitsubstrate is arranged on the inner side of one side wall of the endcase, and the upright portion and the connection plate are weldedtogether through an aperture formed in one side wall of the end caseopposite the upright portion. With this structure, the connection pathis made short and the connection resistance is reduced. Also, theelectrical connection is established with good working efficiency,ensuring high productivity.

Preferably, the battery case serves as an electrode terminal of onepolarity and an electrode terminal of the other polarity is provided onthe end face in the battery, and one end of a safety protection deviceis connected to the electrode terminal in the end face of the batterycase, while the other end of the safety protection device is connectedto the circuit substrate. This way, the safety protection device such asa temperature fuse or PTC element is interposed between the electrodeterminal and the circuit substrate in contact with or in close proximityto the end face of the battery making use of the space in one side ofthe electrode terminal, so that the electric current is shut off whenthe temperature of the battery rises too high, and thus while thestructure is compact, the safety features are improved.

Second and third connection brackets having upright portions thatoverlap each other are secured to the other end of the safety protectiondevice and the circuit substrate, respectively, and these uprightportions of the second and third connection brackets are welded togetherthrough an aperture opened in the end case. Thus, the circuit substrateand the safety protection device are connected to each other through thesecond and third connection brackets with good productivity by thewelding operation through the aperture in the end case.

The external connection terminal set in the end case should preferablybe of the type that establishes or shuts connection between the batteryand a device to be connected by a connector on the equipment side beinginserted or removed. In a portable electronic equipment or the like thathas a battery accommodating space in which the battery pack is set, theexternal connection terminal of this type supplies power with remarkablyhigher stability as compared to the flat type terminal, to which theelectrode terminal of the equipment is merely abutted. Thus, theexternal connection terminal of this type ensures highly reliable powersupply even in an environment of use in which the equipment may besubjected to vibration or impact, and also is set inside the end caseeasily and compactly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view illustrating major parts of abattery pack according to a first embodiment of the present invention;

FIG. 2A and FIG. 2B illustrate the main structure of the battery packaccording to the first embodiment, FIG. 2A being a partially brokenperspective view taken from the direction of arrow IIA of FIG. 1 andFIG. 2B being a cross-sectional view of the same part;

FIG. 3A and FIG. 3B illustrate the main structure of the battery pack ofthe present invention, FIG. 3A being a cross-sectional view taken alongthe line IIIA-IIIA of FIG. 1, FIG. 9, and FIG. 13 and FIG. 3B being across-sectional view taken along the line IIIB-IIIB of FIG. 1, FIG. 9,and FIG. 13;

FIG. 4A to FIG. 4C are perspective views illustrating the battery packof the present invention in the order of the assembling process steps;

FIG. 5 is a perspective view illustrating an assembling process step ofthe battery pack of the present invention;

FIG. 6 is a perspective view illustrating an assembling process step ofthe battery pack of the present invention;

FIG. 7 is a perspective view illustrating an assembling process step ofthe battery pack of the present invention;

FIG. 8 is a perspective view illustrating the complete battery pack ofthe present invention;

FIG. 9 is an exploded perspective view illustrating major parts of abattery pack according to a second embodiment of the present invention;

FIG. 10 is a partially broken perspective view taken from the directionof arrow X of FIG. 9, illustrating the main structure of the batterypack according to the second embodiment;

FIG. 11 is a cross-sectional view illustrating major parts of a batterypack according to a third embodiment of the present invention;

FIG. 12A and FIG. 12B are cross-sectional views illustrating the processsteps of attaching a screw in the third embodiment;

FIG. 13 is an exploded perspective view illustrating major parts of abattery pack according to a fourth embodiment of the present invention;

FIG. 14A and FIG. 14B illustrate the main structure of the battery packof the fourth embodiment, FIG. 14A being a partially broken perspectiveview taken from the direction of arrow XIVA of FIG. 13 and FIG. 14Bbeing a cross-sectional view of the same part;

FIG. 15A and FIG. 15B illustrate the process steps of welding a couplingpin in the same embodiment, FIG. 15A being a cross-sectional viewillustrating the state before welding and FIG. 15B being across-sectional view illustrating the state after the welding;

FIG. 16A to FIG. 16E are perspective views illustrating various examplesof structures for the coupling pin in the same embodiment; and

FIG. 17A and FIG. 17B illustrate the process steps of another method ofwelding a coupling pin in the same embodiment, FIG. 17A being across-sectional view illustrating the state before welding and FIG. 17Bbeing a cross-sectional view illustrating the state after the welding.

BEST MODES FOR CARRYING OUT THE INVENTION

The battery pack of the present invention will be hereinafter describedwith reference to FIG. 1 to FIG. 17B.

First Embodiment

In FIG. 1, the numeral 1 denotes a prismatic battery having a flatrectangular, rounded rectangular, or oval cross section. The battery 1is structured as a lithium ion battery, containing elements forelectromotive force, i.e., an electrode plate assembly and liquidelectrolyte, inside a battery case 2. The electrode plate assembly ismade of strips of positive and negative electrode plates wound aroundwith a separator interposed therebetween to have a multilayer structure.The positive electrode plate consists of a core material made ofaluminum foil and positive electrode mixture paste coated and dried onthe core material, the negative electrode plate consists of a corematerial made of copper foil and negative electrode mixture paste coatedand dried on the core material, and the separator is made of amicroporous polypropylene film or the like.

An electrode terminal 4 is provided to protrude in the center in one endface 3 of the battery case 2. The electrode terminal 4 extends throughthe end face 3 of the battery case 2 in an insulated and airtightmanner, to serve as the negative electrode terminal of the battery 1.The battery case 2 serves as the positive electrode terminal of thebattery 1.

The numeral 5 denotes a circuit substrate arranged upon the end face 3of the battery case 2, and it includes a charge/discharge safetycircuit. The numeral 6 denotes an end case secured on the end face 3 ofthe battery case 2, with the circuit substrate 5 being accommodatedinside. The end case 6 is attached to the battery, with three externalconnection terminals 7 being set inside. These external connectionterminals 7 are of the type that establishes or shuts connection betweenthe battery and a device to be connected by the connectors on the deviceside being inserted or removed; they are respectively arranged oppositethree suitably spaced connection windows 8, which extend over the topface and one side face at one end of the end case 6. Each externalconnection terminal 7 is formed with a pair of connection legs 7 aextending downwards, and the circuit substrate 5 has correspondingconnection holes 9, through which these connection legs 7 a are extendedfor soldering. Two of the three external connection terminals 7 are forthe positive and negative electrodes, the remaining one being aconnection terminal for detecting resistance for identificationpurposes.

The battery pack 10 is chiefly composed of the above-described battery 1and the end case 6 accommodating the circuit substrate 5, being securedto each other. To securely unite the battery and the end case, as shownin FIG. 1 to FIG. 2B, the end case 6 includes attachment holes 11 atboth ends extending in the vertical direction and having a step 11 anear the bottom end, and screws 12 are inserted in these attachmentholes 11, with the screw heads 12 a being engaged with the steps 11 a,and the screw tips are driven into one end face 3 at both ends of thebattery case 2.

This screw tightening is described in more detail below with referencemainly to FIG. 2B. The battery case 2 is made of aluminum or an aluminumalloy including its end face 3. The end face 3 has a relatively largethickness of, for example, about 0.8 to 1.5 mm. At either end of the endface 3, a circular indentation 3 a is press-formed as a screw pilot holeso that the screw 12 is turned into the hole while forming femalethreads. For example, if the screw 12 has metric fine screw threads witha nominal diameter of 1.2 mm, the screw thread height is 0.13 mm and thescrew pitch is 0.25 mm. If the circular indentation 3 a has an insidediameter of 0.9 mm and a depth of 1.4 mm, the screw 12 will engage intothe indentation 3 a about four threads, whereby, if the end face 3 ismade of aluminum or an aluminum alloy, the screw 12 is attached with anecessary strength in the axial direction.

The specification of the screw 12 given above is only an example, andany of fine thread screws with a nominal diameter ranging from 1.0 to2.0 mm and a screw pitch ranging from 0.2 to 0.4 mm may preferably beused. Correspondingly, the circular indentation 3 a may vary in itsinside diameter from 0.6 to 1.7 mm, and in its depth from 0.8 to 1.6 mm.

Next, the electrical connection structure of this battery pack 10 willbe described. The battery case 2, which is the positive electrode, isconnected to the circuit substrate 5 through a first connection bracket13 and a connection plate 14. The first connection bracket 13 is securedto one end face of the battery by welding, and has an upright portion 13a on one side. This upright portion 13 a extends upwards, making contactwith the inner face of one side wall of the end case 6, as shown in FIG.3A. The connection plate 14 is arranged on the circuit substrate 5 sothat it makes surface contact with the inner face of the upright portion13 a of the first connection bracket 13. A connection leg 14 a extendingdownward from the bottom fits in a connection notch 15 formed to oneside of the circuit substrate 5, and is soldered to a connectionelectrode formed on the underside of the connection notch 15. The endcase 6 includes a support wall 6 b for supporting the connection plate14 from inside. The end case 6 also includes an aperture 6 a providedfor the processing purpose in one side wall opposite the upright portion13 a. A pair of welding electrodes are pressed against the uprightportion 13 a of the first connection bracket 13 through this aperture 6a and a welding current is applied across the electrodes, so that theupright portion 13 a and the connection plate 14 are welded together toestablish electrical connection.

The negative electrode terminal 4 is connected to the circuit substrate5 through a safety protection device 16 such as a temperature fuse and aPTC element. More specifically, a connection piece 16 a at one end ofthe safety protection device 16 is connected to the electrode terminal 4by welding, and another connection piece 16 b at the other end of thesafety protection device 16 is securely welded to a second connectionbracket 17, which has an upright portion 17 a on one side. As shown inFIG. 1 and FIG. 3B, a third connection bracket 18, which has an uprightportion 18 a that overlaps the inner face of the upright portion 17 a,is securely welded to the circuit substrate 5. These upright portions 17a and 18 a of the connection brackets 17 and 18 are welded togetherthrough apertures 19 provided for the processing purpose across the endcase 6 in the width direction at the position corresponding to theseupright portions 17 a and 18 a. Thus the negative electrode terminal 4is connected to the circuit substrate 5 through the safety protectiondevice 16 and the connection brackets 17 and 18. The electricalconnection structure of the battery pack 10 of this embodiment has beendescribed with reference to FIG. 3A and FIG. 3B, which are crosssections taken in the direction of arrows IIIA-IIIA and IIIB-IIIB inFIG. 1, respectively. Note, FIG. 3A is also a cross section taken in thedirection of arrows IIIA-IIIA in FIG. 9 and FIG. 13, and FIG. 3B is alsoa cross section taken in the direction of arrows IIIB-IIIB in FIG. 9 andFIG. 13, since the other embodiments to be described later and shown inFIG. 9 and FIG. 13 have the same electrical connection structure as thebattery pack 10 of this embodiment.

Referring to FIG. 1, a first insulation plate 20 is arranged between oneend face 3 of the battery case 2 and the safety protection device 16,and fixedly attached to the end face by adhesive provided on itsunderside. The first insulation plate 20 is formed with a through hole21 in the center through which the electrode terminal 4 extends, and aheat conducting aperture 28 at a position corresponding to the elementpart of the safety protection device 16 so that the element part facesthe end face 3 of the battery case 2. An adhesive 23 is applied on theupper face at the other end of the safety protection device 16 where theconnection piece 16 b is provided, to retain the connection piece 16 bin position. The heat conducting aperture 28 is filled with silicone 24as shown in FIG. 4B so that heat from the battery 1 is efficientlyconducted to the element part. A second insulation plate 25 is arrangedon and bonded to the safety protection device 16 with an adhesiveprovided on its underface, so as to secure insulation between the safetyprotection device 16 and the circuit substrate 5.

Next, the assembling process of the thus structured battery pack 10 willbe described. First, the first insulation plate 20 is placed on andbonded to the end face 3 of the battery 1, as shown in FIG. 4A. Next,the heat conducting aperture 28 of the first insulation plate 20 isfilled with silicone 24 as shown in FIG. 4B, the safety protectiondevice 16 is placed on the first insulation plate 20, and the connectionpiece 16 a at one end is welded to the electrode terminal 4, with thesecond connection bracket 17 being welded to the connection piece 16 bat the other end. The first connection bracket 13 is welded to a sideportion of the first insulation plate 20 that is on the end face of thebattery 1. Next, as shown in FIG. 4C, the second insulation plate 25 isplaced over and bonded to the safety protection device 16 and the firstconnection bracket 13.

Meanwhile, the external connection terminals 7 are set in predeterminedpositions in the end case 6 where they face the connection windows 8, asshown in FIG. 1, and the connection plate 14 is inserted between theaperture 6 a in one side wall and the support wall 6 b. The thirdconnection bracket 18 is welded to a predetermined position on thecircuit substrate 5. Next, the circuit substrate 5 is inserted from thebottom opening of the end case 6, the ends of the connection legs 7 a ofthe external connection terminals 7 protruding through the connectionholes 9 are soldered to the electrodes formed around the connectionholes 9, and the end of the connection leg 14 a of the connection plate14 protruding from the connection notch 15 is soldered to the electrodeformed around the connection notch 15.

Next, as shown in FIG. 5, the end case 6 accommodating the circuitsubstrate 5 inside is coupled onto the end face 3 of the battery 1, sothat the upright portion 13 a of the first connection bracket 13 makessurface contact with the outer face of the connection plate 14, and theupright portion 17 a of the second connection bracket 17 makes surfacecontact with the outer face of the upright portion 18 a of the thirdconnection bracket 18. Screws 12 are inserted into the attachment holes11. A nail hook 26 is bonded to the other end face 1 b of the battery 1,which is a nail catch for allowing easy removal of the battery pack 10.

Next, as shown in FIG. 6, a screw driver (tool) is inserted into theattachment holes 11 at both ends of the end case 6 as indicated by thearrows a to engage with the heads 12 a of the screws 12, and by rotatingthe screw driver while applying pressure, the tips of the screws 12 areengaged into the circular indentations 3 a formed in the end face 3 ofthe battery 1 while forming female threads in the inner peripheralsurface of the indentations, so that the both ends of the end case 6 aresecured to the battery 1 through the screws 12. Welding electrodes areinserted from both sides into the apertures 19 in the end case 6 asindicated by the arrows b, and by applying a welding current andpressure, the upright portions 17 a and 18 a of the connection brackets17 and 18 are welded together (see FIG. 3B). Also, a pair of weldingelectrodes are inserted into the aperture 6 in the end case 6 asindicated by the arrows c and abutted on the upright portion 13 a of thefirst connection bracket 13, and by applying a welding current andpressure, the first connection bracket 13 and the connection plate 14are welded together (see FIG. 3A).

Next, as shown in FIG. 7, an outer label 27, which is a synthetic resinsheet with an adhesive applied on its back side, is wound around andbonded to the circumferences of the battery 1, the lower part of the endcase 6, and the nail hook 26. Sealing pieces 27 a, 27 b, 27 c extendfrom the upper edge of the outer label 27 at positions corresponding tothe attachment holes 11 and the apertures 19 and 6 a in the upper partof the end case 6, and these sealing pieces 27 a, 27 b, 27 c are bondedalong the surface of the end case 6 so that the holes 11 and theapertures 19 and 6 a are covered. Thus, as shown in FIG. 8, the batterypack 1 is complete.

The battery pack 10 of this embodiment has a compact structure since theend case 6 is secured to one end of the battery 1 by tightening thescrews 12 and the case does not accommodate the whole of the battery 1and the circuit substrate 5. Also the connection resistance is reducedbecause the connection path between the battery 1 and the circuitsubstrate 5 and the external connection terminals 7 inside the end case6 is made shorter.

The battery 1 and the end case 6 are securely coupled together by asimple process step of engaging the tip of the screw 12 into thecircular indentation 3 a in the end face 3 of the battery 1, andtherefore the battery pack 10 achieves both high reliability andproductivity. Since the end case 6 is secured to the end face 3 of thebattery 1 with screws 12, the battery pack resists a large force appliedin a direction parallel to the end face 3 of the battery 1 (sheardirection to the screw 12), as well as a large force that acts toseparate the end case 6 from the battery 1 (screw pulling direction) bythe screw thread engagement, and therefore the battery pack has highstrength to external forces from all directions. Further, because thescrews 12 are forced into the end face 3 of the battery 1 while formingfemale threads, when the battery pack 10 is disassembled once byloosening the screws 12 and removing the end case 6, it cannot bere-assembled because the female threads are damaged. This preventsproduction of fake battery packs with reused batteries, and preventsfake products that lack safety standards from going into the market.

The battery case 2 serves as the positive electrode terminal and thenegative electrode terminal 4 of the battery 1 is provided on its endface 3; the first connection bracket 13 is secured to the end face 3 ofthe battery case 2, the connection plate 14 that is partly connected tothe circuit substrate 5 is arranged on the inner side of one side wallof the end case 6, and the upright portion 13 a of the first connectionbracket 13 and the connection plate 14 are welded together through theaperture 6 a formed in the end case 6. The positive electrode of thebattery 1 and the circuit substrate 5 are therefore electricallyconnected with good working efficiency and high productivity is therebyachieved. Also, the connection path can be made short and the connectionresistance is reduced.

One end of the safety protection device 16 is connected to the electrodeterminal 4 on one end face 3 of the battery 1, and the other end of thesafety protection device 16 is connected to the circuit substrate 5. Thesafety protection device 16 such as a temperature fuse and a PTC elementis interposed between the electrode terminal 4 and the circuit substrate5 in contact with or in close proximity with the end face 3 of thebattery 1 making use of the space in one side of the electrode terminal4, so that the electric current is shut off when the temperature of thebattery 1 rises too high, and thus while the structure is compact, thesafety features are improved.

The second and third connection brackets 17 and 18 having uprightportions 17 a and 18 a that overlap with each other are secured to theother end of the safety protection device 16 and the circuit substrate5, respectively, and these upright portions 17 a and 18 a of theconnection brackets 17 and 18 are welded together through the apertures19 opened in the end case 6, and thus the circuit substrate 5 and thesafety protection device 16 are connected to each other with goodproductivity through these connection brackets 17 and 18 by welding.Alternatively, the safety protection device 16 may be omitted, and theelectrode terminal 4 and the circuit substrate 5 may be connected toeach other through a connection bracket(s).

The external connection terminals 7 set inside the end case 6 are of thetype that establishes or shuts connection between the battery andequipment by the connectors on the equipment side being inserted orremoved. In a portable electronic equipment or the like that has abattery accommodating space in which the battery pack 10 is set, theexternal connection terminals 7 of this type ensure highly reliablepower supply even in an environment of use in which the equipment issubjected to vibration or impact. Also, even this type of the externalconnection terminals 7 is set inside the end case 6 easily andcompactly.

While the screw 12 in this embodiment only has the function of securelyattaching the end case 6 to the battery 1 and does not have the functionof electrically connecting the battery case 2 with the circuit substrate5, one alternative is to make the head 22 a of the screw 12 to contactthe electrode on the circuit substrate 5, or, if necessary, to connectpart of the head 12 a to the electrode by laser beam welding, so as toestablish electrical connection at the same time. This makes the firstconnection bracket 13 and the connection plate 14 redundant and thestructure is further simplified.

Second Embodiment

A second embodiment of the invention is described next. The elementsthat are common to the above-described first embodiment are given thesame reference numerals and will not be described again, and only thedifferences will be described.

In the first embodiment, the battery case 2 and the end case 6 aresecurely united by forcing the tips of the screws 12 into the end face 3of the battery case 2. In this embodiment, as shown in FIG. 9 and FIG.10, coupling pins 22 with heads 22 a are set in the attachment holes 11at both ends of the end case 6 with the heads 22 a engaging with thesteps 11 a in the attachment holes 11, and the tips of the pins arewelded to the end face 3 at both ends of the battery case 2. The weldingmethod applicable here includes spot welding, arc welding, laser weldingand others, among which spot welding is most preferable because of lowcost and good working efficiency.

The difference between this embodiment and the first embodiment in theassembling process is as follows: In the first embodiment, a screwdriver (tool) was inserted into the attachment holes 11 at both ends ofthe end case 6, and by rotating the screw driver while applying pressureto the screws 12, the tips of the screws 12 were engaged into thecircular indentations 3 a formed in the end face 3 of the battery 1, sothat the end case 6 was securely united with the battery 1. In thesecond embodiment, welding electrodes are inserted into the attachmentholes 11 at both ends of the end case 6 as indicated by the arrows a inFIG. 6, and abutted on the heads 22 a of the coupling pins 22, and byapplying a welding current and pressure, the tips of the coupling pins22 are welded to the end face 3 of the battery 1, so that the both endsof the end case 6 are united to the battery 1 through the coupling pins22. Other process steps are the same as those of the first embodiment.Welding electrodes are inserted from both sides into the apertures 19 inthe end case 6 as indicated by the arrows b, and by applying a weldingcurrent and pressure, the upright portions 17 a and 18 a of theconnection brackets 17 and 18 are welded together (see FIG. 3B). Also, apair of welding electrodes are inserted into the aperture 6 a in the endcase 6 as indicated by the arrows c and abutted on the upright portion13 a of the first connection bracket 13, and by applying a weldingcurrent and pressure, the first connection bracket 13 and the connectionplate 14 are welded together (see FIG. 3A).

According to this embodiment, the battery 1 and the end case 6 aresecurely coupled together by a simple process step of welding the tip ofthe coupling pin 22 to the end face 3 of the battery 1, and the batterypack 10 thereby achieves both high reliability and productivity.

While the coupling pin 22 in this embodiment only has the function ofsecurely attaching the end case 6 to the battery 1 and does not have thefunction of electrically connecting the battery case 2 with the circuitsubstrate 5, one alternative is to connect the head 22 a of the couplingpin 22 to the electrode on the circuit substrate 5 by welding toestablish electrical connection at the same time, so that the firstconnection bracket 13 and the connection plate 14 are made redundant andthe structure is further simplified.

Third Embodiment

A third embodiment of the battery pack of the invention is describednext. The elements that are common to the above described first andsecond embodiments are given the same reference numerals and will not bedescribed again, and only the differences will be described.

In the second embodiment, the tip of the coupling pin 22 was directlyconnected to the end face 3 of the battery case 2 by resistance welding.If, however, the end face 3 of the battery case 2 is made of aluminum oran aluminum alloy while the coupling pin 22 is made of an iron materialsuch as stainless steel or nickel-plated steel so as to securesufficient strength despite its small size, there may be cases where, bythe direct resistance welding method, it is hard to achieve necessaryattachment strength with high reliability. To solve this problem, in thethird embodiment, the end face 3 of the battery case 2 is made of thesame material as the coupling pin 22 at least in the portion to whichthe tip of the coupling pin 22 will be attached.

In this embodiment, as shown in FIG. 11, a screw 31 made of the sametype of material as the coupling pin 22, i.e., stainless steel ornickel-plated steel, is securely tightened to a portion where the tip ofthe coupling pin 22 will be attached in the end face 3 of the batterycase 2, and the tip of the coupling pin 22 is connected to the top ofthe head 31 a of the screw 31 by resistance welding.

More specifically, the sealing plate that forms the end face 3 of thebattery case 2 is made of aluminum or an aluminum alloy, with arelatively large thickness of, for example, about 0.8 to 1.5 mm. Acircular indentation 32 that works as a screw pilot hole, into which thescrew 31 is driven while forming female threads, is formed at either endof the end face 3 of the battery case 2 when press-forming the sealingplate (end face 3) as shown in FIG. 12A, and after that, as shown inFIG. 12B, the screw 31 is engaged into the hole and made in one piecewith the end face 3, so that the top face of the screw head 31 a willform the welding surface at the bottom of the coupling pin 22.

For example, if the screw 31 has metric fine screw threads with anominal diameter of 1.2 mm, the screw thread height is 0.13 mm and thescrew pitch is 0.25 mm. If the circular indentation 32 has an insidediameter of 0.9 mm and a depth of 1.4 mm, the screw 31 will engage intothe indentation 32 about four threads, whereby, even if the end face 3is made of aluminum or an aluminum alloy, the screw 31 is attached witha necessary strength in the axial direction.

The specification of the screw 31 given above is only an example, andany of fine thread screws with a nominal diameter ranging from 1.0 to2.0 mm and a screw pitch ranging from 0.2 to 0.4 mm may preferably beused. Correspondingly, the circular indentation 32 may vary in itsinside diameter from 0.6 to 1.7 mm, and in its depth from 0.8 to 1.6 mm.

As described above, with this embodiment, the screw 31 made of the sametype of material as the coupling pin 22 is secured in the end face 3 ofthe battery case 2 at least in a portion where the tip of the couplingpin 22 will be attached, and the coupling pin 22 is connected to the topface of the screw head 31 a by resistance welding. As the pin and screware both made of the same type of material, they are readily secured toeach other with sufficient strength and high reliability. Also, this isreadily achieved only by adding a simple process step of securelyengaging the screw 31 into the end face 3 of the battery 1.

While the coupling pin 22 in this embodiment only has the function ofsecurely attaching the end case 6 to the battery 1 and does not have thefunction of electrically connecting the battery case 2 with the circuitsubstrate 5, one alternative is to connect the head 22 a of the couplingpin 22 with the electrode on the circuit substrate 5 by welding so as toestablish electrical connection at the same time, so that the firstconnection bracket 13 and the connection plate 14 are made redundant andthe structure is further simplified.

Fourth Embodiment

A fourth embodiment of the battery pack of the invention is describednext. The elements that are common to the above described first to thirdembodiments are given the same reference numerals and will not bedescribed again, and only the differences will be described.

In this embodiment, a coupling pin 42 shown in FIG. 13A to FIG. 14B isused instead of the screw 12 of the first embodiment, the coupling pin22 of the second embodiment, and the combination of the screw 31 and thecoupling pin 22 of the third embodiment. That is, the end case 6includes attachment holes 11 at both ends extending in the verticaldirection and having a step 11 a near the bottom end, and the couplingpins 42 are inserted in these attachment holes 11, with their heads 42 abeing engaged with the steps 11 a, and their tips are secured to one endface 3 of the battery case 2 at both ends by spot welding (resistancewelding) so as to securely unite the battery case 1 and the end case 6.

This spot-welded part at the tip of the coupling pin 42 is described inmore detail below with reference mainly to FIG. 14B, FIG. 15A, and FIG.15B. The battery case 2, including its end face 3, is made of aluminumor an aluminum alloy. The end face 3 has a relatively large thicknessof, for example, about 0.8 to 1.5 mm. At either end of the end face 3, acircular hole 3 a having an inside diameter of about 0.6 to 1.7 mm and adepth of about 0.8 to 1.6 mm is press-formed as shown in FIG. 15A indetail. The hole 3 a need not necessarily be circular and may be square.

The coupling pin 42 should preferably be made of an iron material suchas nickel-plated steel or stainless steel so as to secure sufficientstrength despite its small size. As shown in FIG. 15A in detail, thecoupling pin 42 includes a protrusion 42 b at its tip that fits in thehole 3 a, and a circumferential recess 42 c formed at the base end ofthe protrusion 42 b. Preferably, the coupling pin 42 has an axialdiameter of 1.0 to 2.0 mm, with the protrusion 42 b having a sizecorresponding to the hole 3 a, and the recess 42 c having an axial widthof about one third to half of the depth of the hole 3 a and a radialdepth of about one fifth to one third of the inside diameter of the hole3 a. The shape and number of the recess 42 c may be freely selected fromvarious options: For example, square recesses may be formed at two tofour locations in the circumferential direction as shown in FIG. 16A,circular arc notches may be cut from both sides into the protrusion 42 bas shown in FIG. 16B, a continuous annular groove may be provided aroundthe entire circumference as shown in FIG. 16C, slot grooves may beformed if the protrusion is square as shown in FIG. 16D, and 1 to 2 mmwide and deep recesses 42 c may be formed on the outer face of theprotrusion 42 b as knurling, as shown in FIG. 16E.

As shown in FIG. 15A, with the protrusion 42 b of the coupling pin 42engaging into the hole 3 a in the end face 3 of the battery case 2, awelding electrode is abutted on the head 42 a of the coupling pin 42 ateither end of the end case 6, and by applying a welding current acrossthe coupling pin 42 and the end face 3 of the battery case 2, theinterface between the tip of the coupling pin 42 and the end face 3 ofthe battery case 2 is heated, whereby the end face 3 of the battery case2 that is made of aluminum or an aluminum alloy and thus has a lowmelting point melts and they are welded together. At the same time, themolten metal flows in and fills the recess 42 c of the protrusion 42 bas shown in FIG. 15B and provides an anchoring effect, so that the jointbetween the tip of the coupling pin 42 and the end face 3 of the batterycase 2 is rigid enough to withstand forces from all directions.

While the periphery of the hole 3 a is flush with the end face 3 of thebattery case 2 in the example shown in FIG. 15A and FIG. 15B, onealternative is to form a boss 3 b at the periphery of the hole 3 a whenpress-forming the hole 3 a, as shown in FIG. 17A. The end face aroundthe protrusion 42 b of the coupling pin 42 is abutted on this boss 3 b,so that the welding current is concentrated at this boss 3 b during spotwelding. This melts the boss 3 b easily and causes the molten metal toflow in and fill the recess 42 c smoothly, as shown in FIG. 17B, wherebythe anchoring effect is reliably achieved.

In this embodiment, to securely unite the battery 1 and the end case 6,welding electrodes of a spot welder are inserted in the attachment holes11 at both ends of the end case 6 as indicated by the arrows a in FIG. 6and abutted on the heads 42 a of the coupling pins 42, and by applying awelding current and pressure, the tips of the coupling pins 42 arewelded to the end face 3 of the battery 1, so that the end case 6 issecurely united with the battery 1 at both ends through these couplingpins 42. Other process steps are the same as the other embodiments.Welding electrodes are inserted from both sides into the apertures 19 inthe end case 6 as indicated by the arrows b, and by applying a weldingcurrent and pressure, the upright portions 17 a and 18 a of theconnection brackets 17 and 18 are welded together (see FIG. 3B). Also, apair of welding electrodes are inserted into the aperture 6 a in the endcase 6 as indicated by the arrows c and abutted on the upright portion13 a of the first connection bracket 13, and by applying a weldingcurrent and pressure, the first connection bracket 13 and the connectionplate 14 are welded together (see FIG. 3A).

With this embodiment, the battery 1 and the end case 6 are securelycoupled together by a simple process step of spot welding the tip of thecoupling pin 42 to the end face 3 of the battery 1, and therefore thebattery pack 10 achieves both high reliability and productivity. The tipof the coupling pin 42 is secured to the end face 3 of the battery 1such that the material forming the end face 3 of the battery 1 bitesinto the recess 42 c formed around the protrusion 42 b at the tip of thecoupling pin 42, providing the anchoring effect. Therefore, the batterypack resists a large force applied in a direction parallel to the endface 3 of the battery 1 (shear direction to the coupling pin 42), aswell as a large force that acts to separate the end case 6 from thebattery 1 (pin pulling direction) by the anchoring effect, and thebattery pack has high attachment strength to external forces from alldirections.

While the coupling pin 42 in this embodiment only has the function ofsecurely attaching the end case 6 to the battery 1 and does not have thefunction of electrically connecting the battery case 2 with the circuitsubstrate 5, one alternative is to make the head 42 a of the couplingpin 42 to contact the electrode on the circuit substrate 5, or, ifnecessary, to connect part of the head 42 a to the electrode by laserbeam welding, so as to establish electrical connection at the same time.This makes the first connection bracket 13 and the connection plate 14redundant and the structure is further simplified.

INDUSTRIAL APPLICABILITY

As described above, the battery pack of the present invention has acompact structure since the end case is secured to one end of thebattery in a manner that exhibits a high resistance to external forcesfrom all directions. Also, the connection path between the battery andthe circuit substrate and the external connection terminals inside theend case is made shorter, and the connection resistance is reduced. Thebattery and the end case are securely united by a simple process step,such as forcing the tip of a screw into the end face of the battery,welding the tip of a coupling pin to the end face of the battery,forcing the tip of a screw into the end face of the battery and weldinga coupling pin to the screw head, or welding the tip of a coupling pinto the end face of the battery in a manner that provides an anchoringeffect. Thus the invention realizes a battery pack that achieves bothhigh reliability and productivity, and is applicable to production ofsmall battery packs for use in portable electronic equipment.

1. A battery pack comprising: a battery; a circuit substrate having acharge/discharge safety circuit and arranged on one end face of thebattery; and an end case in which an external connection terminal isset, wherein the circuit substrate is arranged inside the end case, theend case includes attachment holes at both ends thereof extendingtherethrough and each attachment hole includes a step near the bottomend thereof, and the end case is secured to the battery by screws, eachwith a screw head, the screw head extending through a respectiveattachment hole and engaging with the step in the attachment hole in theend case at both ends and tips of the screws being engaged into the endface at both ends of the battery; and the battery case serves as anelectrode terminal of one polarity and an electrode terminal of theother polarity is provided on the end face in the battery; a firstconnection bracket having an upright portion is secured to the end faceof the battery case; a connection plate that makes surface contact withthe upright portion of the first connection bracket and that is partlyconnected to the circuit substrate is arranged on the inner side of oneside wall of the end case; and the upright portion and the connectionplate are welded together through an aperture formed in one side wall ofthe end case opposite the upright portion.
 2. The battery pack accordingto claim 1, wherein: one end of a safety protection device is connectedto the electrode terminal in the end face of the battery case and theother end of the safety protection device is connected to the circuitsubstrate.
 3. The battery pack according to claim 2, wherein: second andthird connection brackets having upright portions that overlap eachother are secured to the other end of the safety protection device andthe circuit substrate, respectively; and the upright portions of thesecond and third connection brackets are welded together through anaperture opened in the end case.
 4. The battery pack according to claim1, wherein the external connection terminal set in the end case is ofthe type that establishes or shuts connection between the battery and adevice to be connected by a connector on the device side being insertedor removed.
 5. A battery pack comprising: a battery, a circuit substratehaving a charge/discharge safety circuit and arranged on one end face ofthe battery; and an end case in which an external connection terminal isset, wherein the circuit substrate is arranged inside the end case, theend case includes attachment holes at both ends thereof extendingtherethrough and each attachment hole includes a step near the bottomend thereof, and the end case is secured to the battery by coupling pinswith heads, the heads of the coupling pins extending through arespective attachment hole and engaging with the step in the attachmenthole in the end case at both ends and the tips of the coupling pinsbeing secured to the end face at both ends of the battery; and thebattery case serves as an electrode terminal of one polarity and anelectrode terminal of the other polarity is provided on the end face inthe battery; a first connection bracket having an upright portion issecured to the end face of the battery case; a connection plate thatmakes surface contact with the upright portion of the first connectionbracket and that is partly connected to the circuit substrate isarranged on the inner side of one side wall of the end case: and theupright portion and the connection plate are welded together through anaperture formed in one side wall of the end case opposite the uprightportion.
 6. The battery pack according to claim 5, wherein the end faceof the battery at least in a portion thereof to which the tip of thecoupling pin is attached is provided with the same type of material asthe coupling pin.
 7. The battery pack according to claim 6, wherein theend face of the battery in a portion opposite the tip of the couplingpin is provided with the same type of material as the coupling pin. 8.The battery pack according to claim 5, wherein: one end of a safetyprotection device is connected to the electrode terminal in the end faceof the battery case and the other end of the safety protection device isconnected to the circuit substrate.
 9. The battery pack according toclaim 8, wherein: second and third connection brackets having uprightportions that overlap each other are secured to the other end of thesafety protection device and the circuit substrate, respectively; andthe upright portions of the second and third connection brackets arewelded together through an aperture opened in the end case.
 10. Thebattery pack according to claim 5, wherein the external connectionterminal set in the end case is of the type that establishes or shutsconnection between the battery and a device to be connected by aconnector on the device side being inserted or removed.
 11. A batterypack comprising: a battery; a circuit substrate having acharge/discharge safety circuit and arranged on one end face of thebattery; and an end case in which an external connection terminal isset, wherein the circuit substrate is arranged inside the end case, theend case includes attachment holes at both ends thereof extendingtherethrough and each attachment hole includes a step near the bottomend thereof, and the end case is secured to the battery by a couplingpin with heads, the heads extending through a respective attachment holeand engaging with the step in the attachment hole in the end case, suchthat the material forming the end face of the battery bites into arecess formed in an outer periphery at the tip of the coupling pin tosecure the tip of the coupling pin to the end face of the battery; andthe battery case serves as an electrode terminal of one polarity and anelectrode terminal of the other polarity is provided on the end face inthe battery; a first connection bracket having an upright portion issecured to the end face of the battery case; a connection plate thatmakes surface contact with the upright portion of the first connectionbracket and that is partly connected to the circuit substrate isarranged on the inner side of one side wall of the end case; and theupright portion and the connection plate are welded together through anaperture formed in one side wall of the end case opposite the uprightportion.
 12. The battery pack according to claim 11, wherein: thecoupling pin includes a protrusion at the tip that has the recess in itsperipheral surface; the end face of the battery includes a hole to whichthe protrusion at the tip of the coupling pin fits; and with theprotrusion being fitted in the hole, the tip of the coupling pin and theend face of the battery are joined together by resistance welding. 13.The battery pack according to claim 11, wherein: one end of a safetyprotection device is connected to the electrode terminal in the end faceof the battery case and the other end of the safety protection device isconnected to the circuit substrate.
 14. The battery pack according toclaim 13, wherein: second and third connection brackets having uprightportions that overlap each other are secured to the other end of thesafety protection device and the circuit substrate, respectively; andthe upright portions of the second and third connection brackets arewelded together through an aperture opened in the end case.
 15. Thebattery pack according to claim 11, wherein the external connectionterminal set in the end case is of the type that establishes or shutsconnection between the battery and a device to be connected by aconnector on the device side being inserted or removed.